Global Warming Kills Trees, and People

Article excerpt

In 1992 a provocative editorial in The Lancet questioned that while environmental pollution kills trees, does it kill people? (1). As was to be expected, it stimulated a series of letters documenting a clear link to human health, primarily via ambient air pollution, which was a major concern at the time. In the last decade, increasing evidence has accumulated on the impacts of "environmental change"--often large-scale changes such as biodiversity loss, climate change and desertification. These changes are known to kill trees, and a recent article attributes an increase in the spruce bark beetle population to the warmer climate in Alaska (2).

But does climate change or biodiversity loss really kill people? This is a difficult question because global environmental changes involve a multitude of direct and indirect exposure pathways. While public health practitioners may feel they lack the tools to assess risks or to implement necessary interventions, new scientific insights are beginning to provide a clearer view of future health risks and options for prevention.

One type of environmental change that has received attention and led to clear interventions has been the increase in ultraviolet radiation resulting from the depletion of stratospheric ozone (3). Epidemiological studies show a straight-forward dose-response relationship between sun exposure and skin cancer (4) and cataracts (5). Public health campaigns to reduce sun exposure, particularly in vulnerable groups and at critical time periods, have resulted from this scientific finding.

However, the health consequences of many environmental changes occur through less direct mechanisms, and this fact makes their study more difficult. It is easier to envisage a cancer death associated with ultraviolet radiation exposure than death as the result of climate change or biodiversity loss. Heat-related mortality is an exception, because it is clearly a direct health effect of climate extremes. In 2003 an unprecedented heatwave hit France, causing more than 14 800 excess deaths and representing a 60% increase in expected mortality (6).

Other health outcomes (mostly adverse) stemming from climate change may occur through more complex pathways including, for example, malnutrition, diarrhoeal diseases, respiratory illness, some vector-borne diseases, and flood-related injuries (7, 8). WHO has quantified some of these population-wide health risks. Based on detailed temperature and precipitation data globally, WHO estimates that approximately 150 000 deaths in 2000 can be attributed to changes in global climate experienced over the preceding decade (9). …